Auxiliary Content Synchronization Protocol and Auxiliary Resource Presentation List are not words that easily roll off the tongue. Even among users of these two standards, the term CSP/RPL is used when describing them. CSP/RPL describes a communication method for synchronizing an auxiliary content server, or ACS, to a digital cinema server, or DCS. It is the standardized way to synchronize closed captions. If you can follow the acronyms, the RPL tells the ACS where the closed caption text file is located within the DCS. The ACS then pulls the file. At the same time, the ACS receives its synchronization and control information through the CSP protocol. The result is that the correct closed caption is transferred to the auxiliary server, which is then plays the caption in sync with the movie.
It is one of the small miracles of the industry that all server manufacturers implement CSP/RPL, even though it wasn’t introduced until the 2007-2008 timeframe. Not all manufacturers implement it with a similar set of behaviors, however. To overcome this, USL, a maker of closed caption devices, wrote a wiki blog over a year ago to fill in the implementation gaps that are not covered by standards. That work is now receiving some polish, and will be presented in the next ISDCF meeting.
Up until recently, USL has been the only manufacturer to sell a closed caption ACS. Doremi’s Captiview closed caption system did not use CSP/RPL when first introduced, opting instead to eliminate the ACS role by implementing the synchronization function internal to the digital cinema server. However, Doremi now has several thousand screens installed with Captiview, and not all of its customers have a Doremi server for every screen. As a result, Doremi has now taken the wraps off of its AccessLink box, which is its version of an ACS, driven by CSP/RPL. It won’t be found in Doremi’s price list, as it’s considered to be a custom product. But it is a product, nonetheless, and it deserves to be seen in the next ISDCF Plugfest. With two manufacturers of a closed caption ACS, some competitive behavior can begin.